Aircraft are provided with a substantial number of outwardly exposed, flush mounted panels. Typically, these panels are removable or hinged to the surrounding surface of the aircraft to provide, for example, an opening for accessing the engine of the aircraft, particularly for maintenance thereon. Various types and designs of latch assemblies have been used to secure these flush mounted panels in place.
One such latch assembly is the over center hook latch as shown, for example, in U.S. Pat. No. 2,712,955. In this particular latching assembly, the fulcrum axis of the latch handle is mounted to a bracket on the aircraft panel and the latch hook engages a keeper on the aircraft structure. The latch is designated as an over center latch because, in the closed position, the load on the latch handle creates a moment arm on the latch handle about the fulcrum axis in a direction which maintains the latch in its closed position.
Known over center latch assemblies have primarily emp1oyed lever arms or cam action to provide the necessary pull-up force required to bring the complementary panel components together. While operationally quite efficient, these arrangements do possess certain definite disadvantages. Due to high operational friction, the pull-up capabilities of the latch assemblies of the type concerned here are poor, thus often requiring the exertion of an inordinate amount of force in order to operate the latch.
Another disadvantage of the known latch assemblies, such as that disclosed by U.S. Pat. No. 4,053,177, is that the upper surface of the latch handle is mounted so as to be flush with the outer skin of the aircraft when the latch is in the closed position. While this configuration does mitigate air flow disturbances in the vicinity of the latch assembly, the resulting external surface roughness of this type of flush mounted latch assembly generates large surface area aerodynamic disturbances which increase drag as well as cause undesirable flow characteristics.
Additionally, due to the high forces exerted on the suface of the aircraft, proper adjustment between the hook latch and corresponding keeper arm is critical and must be maintained. If the distance is too great, the latch either will not close or will create excessive compressional forces on the aircraft components resulting in possible damage to the components or latch. If the distance is too close, the hook will not engage the keeper with suitable tension to maintain the panel on the aircraft, thus resulting in a questionable locking condition.
Because of the possible damage or even total loss of an aircraft should the latch fail. great care is exercised to make sure that the latch is secure and that any play or free movement between the hook latch and its keeper is eliminated. While latching assemblies are known having means for providing such adjustment when the latch is either engaged or disengaged, poor adjustment capabilities have resulted due to the limited amount of adjustable travel offered by the known adjustment arrangements.
Also, the known latching assemblies are, typically, configured with numerous moving parts which not only diminish the reliability of operation of the latch, but also make the replacement of the component parts of the latch difficult, particularly while the latch assembly is installed in the panel. Furthermore, the the feature of a secondary locking capability incorporated into the normal operation of the latch to provide back-up locking is, heretofore, unknown.